1. Field of the Invention
The present invention relates to a pressure measuring system for a vacuum chamber, in particular, to a pressure measuring system for a vacuum chamber using ultrasonic wave.
2. Background of the Related Art
In general, vacuum chambers used in the fabrication process of the semiconductor and the LCD are at low vacuum state in the range of 1 Pa˜105 Pa, and the pressure measurement of such a low vacuum region is performed by using a CDG (capacitance diaphragm gauge).
Accordingly, the vacuum pressure measurement from now on has been performed by mounting such sensor or measuring device in a vacuum chamber. However, when several sensors are to be mounted in such chamber, possibility of the leakage of the vacuum at a connection portion, and the like becomes very high. As a result, the vacuum leakage should be always checked before the use of the vacuum chamber, or measuring the vacuum pressure.
Further, it was required to form a vacuum state in the inside of the chamber, and the like, in which the vacuum pressure sensor or the measuring device was not mounted, after separately mounting it inside of them. In addition, it was impossible to measure the vacuum pressure, if it was impossible to mount such sensor or measuring device, or it was impossible to perform the separate mounting work of it.